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1
Elfsberg, Jessica. "Oscillation Mark Formation in Continuous Casting Processes." Licentiate thesis, KTH, Casting of Metals, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1653.
Testo completo
2
Vijaykumar, Adithya. "Smoothed Particle Hydrodynamics Simulation for Continuous Casting." Thesis, KTH, Matematik (Inst.), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105554.
Testo completoAbstract (sommario):
This thesis proposes a way of simulating the continuous casting process of steel using Smoothed Particle Hydrodynamics (SPH). It deals with the SPH modeling of mass, momentum and the energy equations. The interpolation kernel functions required for the SPH modeling of these equations are calculated. Solidification is modeled by some particles are used to represent fluids and others solids. Elastic forces are calculated between the particle neighbors to create deformable bodies. The fluid solidifies into the elastic body when it cools down and the elastic body melts as it is heated. In continuous casting the molten metal solidifies forming a shell when it comes in contact with the cold wall. The mold of the continuous casting is modeled with a cold oscillating wall and a symmetric wall. Once the shell is formed water is sprayed on the solidified metal. If the shell is thin and cooling is not sufficient, the elastic body melts due to the effect of the hot fluid.<br>Den klassiska SPH-modellen för vätskor med fri yta kompletteras med värmeledning med fasomvandling och stelning: partiklar kan byta mellan vätske-tillstånd och solid-tillstånd beroende på temperaturen. Elastiska krafter beroende på avstånd mellan partiklarna aktiveras i solid-tillståndet och slås av i fluid-tillstånd så att vätskan kan stelna och senare smälta igen om så behövs. Vid stränggjutning stelnar smältan, som fylls på via ett rör, vid kontakt med en oscillerande, kall kokill-vägg, till ett elastiskt skal. Detta kyls fortlöpande genom påsprutning av vatten utanpå kokillen och direkt på skalet, som förångas. Skalet deformeras nedanför kokillen av det hydrostatiska trycket från smältan; om det ar för tunt brister det. Som demonstration gjordes en simulering där ett skal skapas, varpå man slår av vattenkylningen på ett parti: då smälter skalet och blir tunnare och till sist brister det och all smälta rinner ut genom hålet. Noggrannheten i simuleringen lämnar en del att önska men det vore mycket svårt att bygga en så komplex modell med vanlig CFD.
3
Pieskä, J. (Jali). "Domain decomposition methods for continuous casting problem." Doctoral thesis, University of Oulu, 2004. http://urn.fi/urn:isbn:9514274679.
Testo completoAbstract (sommario):
Abstract
Several numerical methods and algorithms, for solving the mathematical model of a continuous casting process, are presented, and theoretically studied, in this work. The numerical algorithms can be divided in to three different groups: the Schwarz type overlapping methods, the nonoverlapping Splitting iterative methods, and the Predictor-Corrector type nonoverlapping methods. These algorithms are all so-called parallel algorithms i.e., they are highly suitable for parallel computers.
Multiplicative, additive Schwarz alternating method and two asynchronous domain decomposition methods, which appear to be a two-stage Schwarz alternating algorithms, are theoretically and numerically studied. Unique solvability of the fully implicit and semi-implicit finite difference schemes as well as monotone dependence of the solution on the right-hand side are proved. Geometric rate of convergence for the iterative methods is investigated.
Splitting iterative methods for the sum of maximal monotone and single-valued monotone operators in a finite-dimensional space are studied. Convergence, rate of convergence and optimal iterative parameters are derived. A two-stage iterative method with inner iterations is analyzed in the case when both operators are linear, self-adjoint and positive definite.
Several new finite-difference schemes for a nonlinear convection-diffusion problem are constructed and numerically studied. These schemes are constructed on the basis of non-overlapping domain decomposition and predictor-corrector approach. Different non-overlapping decompositions of a domain, with cross-points and angles, schemes with grid refinement in time in some subdomains, are used. All proposed algorithms are extensively numerically tested and are founded stable and accurate under natural assumptions for time and space grid steps.
The advantages and disadvantages of the numerical methods are clearly seen in the numerical examples. All of the algorithms presented are quite easy and straight forward, from an implementation point of view. The speedups show that splitting iterative method can be parallelized better than multiplicative or additive Schwarz alternating method.
The numerical examples show that the multidecomposition method is a very effective numerical method for solving the continuous casting problem. The idea of dividing the subdomains to smaller subdomains seems to be very beneficial and profitable. The advantages of multidecomposition methods over other methods is obvious. Multidecomposition methods are extremely quick, while being just as accurate as other methods. The numerical results for one processor seem to be very promising.
4
Bagha, Shahin. "Continuous casting mould fluxes : simulation and characterisation." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37624.
Testo completo
5
Elsawy, Abdel Raouf. "Net shape continuous casting of cored rods." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28872.pdf.
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6
Blase, Thomas Albert. "Development of a continuous wire casting technique." Thesis, Queen Mary, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515460.
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7
CIPRIANO, LUIZ CARLOS. "NUMERICAL SIMULATION OF THE CONTINUOUS CASTING PROCESS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1988. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33279@1.
Testo completoAbstract (sommario):
O processo de lingotamento contínua de metais é simulado numericamente. Placas ou tarugos metálicos são produzidos continuamente, mantendo-se o escoamento do material através do molde. A frente de solidificação depende da velocidade de retirada de material e da refrigeração imposta na superfície do lingote. A posição da interface líquido-sólido e o campo de temperaturas na região sólida são determinados, e consideram-se os efeitos da velocidade na curvatura da interface. É analisado um modelo retangular bi-dimensional e a equação da energia é resolvida utilizando-se o método numérica de diferenças finitas das volumes de controle. Os resultados são comparados com soluções analíticas simplificadas onde a termo de transporte não foi considerado e mostram que o calar transportado pelo movimento de lingote tem influência significativa na forma da interface e em sua localização dentro do molde durante o processo.<br>This work deals with a numerical simulation of the continuous casting process. This process is employed in the fabrication of metallic inguts. The position of the solid-liquid interface is determined together with the temperature field in the solid region. The research is facused on studying the effect of the withdrawal velocity on the interface position, aiming at accidental leakage preventien during the process. In this
analysis, the sensible heat is taken into acceunt, in contrast to previous marks reported in the open literature. The present work employed a two-dimensional model. The energy equation was integrated in the rectangular domain by means of the finite-volume method. The liquid regions was at the fusion temperatures, whereas one of the side boundaries was strogly cooled to promote solidification. An algorithm was developed to determine the interface pesition and the domain length. Comparisons of this results obtained with the available solutions obtained excluding sensible heat showed that, depending upon the value of the withdrawal velocity, the sensible heat may or may not be negleted. The simulations was performed with the aid of a microcomputer of the IBM-PC/XT type, employing the Fortran language.
8
Machingawuta, Noel Chenjerayi. "Continuous casting mould fluxes : constitution and properties." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47164.
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9
Sinha, Asish Kumar. "Melt flow and cleanliness in continuous casting tundishes /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487686243820661.
Testo completo
10
Nazem, Jalali Pooria. "Analysis of Different Continuous Casting Practices Through Numerical Modelling." Thesis, KTH, Materialvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-161559.
Testo completoAbstract (sommario):
Fluid flow accompanied by heat transfer, solidification and interrelated chemical reactions play a key role during Continuous Casting (CC) of steel. Generation of defects and production issues are a result of the interaction between mould flux, steel grade and casting conditions. These issues are detrimental to both productivity and quality. Thus, the development of reliable numerical models capable of simulating fluid flow coupled to heat transfer and solidification are in high demand to assure product quality and avoid defects. The present work investigates the influence of steel grade, mould powder and casting conditions on process stability by including heat and mass transfer through liquid steel, slag film layers and solidifying shell. The thesis addresses the application of a numerical model capable of coupling the fluid flow, heat transfer and solidification developed by Swerea MEFOS; based on the commercial CFD code FLUENT v12. The Volume of Fluid (VOF) method, which is an interface tracking technique, is coupled to the flow model for distinction of the interface between steel and slag. The current methodology not only allows the model to describe the behaviour of molten steel during solidification and casting but also makes the assessment of mould powders performance possible. Direct prediction of lubrication efficiency, which is demonstrated by solid-liquid slag film thickness and powder consumption, is one of the most significant advantages of this model. This prediction is a direct result of the interaction between metal/slag flow, solidification and heat transfer under the influence of mould oscillation and transient conditions. This study describes the implementation of the model to analyse several steel and mould powder combinations. This led to detection of a combination suffering from quality problems (High Carbon Steel + High Break Temperature Powder) and one, which provides the most stable casting conditions (Low Carbon Steel + Low Break Temperature Powder). Results indicate the importance of steel pouring temperature, mould powder break temperature and also solidification range on the lubrication efficiency and shell formation. Simulations illustrate that Low Carbon Steel + Low Break Temperature Powder delivers the best lubrication efficiency and thickest formed shell. In contrast, High Carbon Steel + High Break Temperature Powder conveys the minimum lubrication efficiency. Therefore, it was concluded that due to absence of proper powder consumption and solidification rate the latter combination is susceptible to production defects such as stickers and breakouts during the casting sequence.
11
Ogbogu, S. O. E. "Electromagnetic stirring in the continuous casting of molten metal." Thesis, University of Bradford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374933.
Testo completo
12
Matys, Paul. "Fluid flow and heat transfer in continuous casting processes." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28504.
Testo completoAbstract (sommario):
A three-dimensional finite difference code was developed to simulate fluid flow and heat transfer phenomena in continuous casting processes.
The mathematical model describes steady state transport phenomena in a three dimensional solution domain that involves: turbulent fluid flow, natural and forced convection, conduction, release of latent heat at the solidus surface, and tracing of unknown location of liquid/solid interface.
The governing differential equations are discretized using a finite volume method and a hybrid central, upwind differencing scheme. A fully three-dimensional ADI-like iterative procedure is used to solve the discretized algebraic equations for each dependent variable. The whole system of interlinked equations is solved by the SIMPLE algorithm.
The developed computer code was used for parametric studies of continuous casting of aluminum. The results were compared against available experimental data. This numerical simulation enhances understanding of the fluid flow and heat transfer phenomena in continuous casting processes and can be used as a tool to optimize technologies for continuous casting of metals.<br>Applied Science, Faculty of<br>Mechanical Engineering, Department of<br>Graduate
13
Löfgren, Hans B. "Theoretical magnetohydrodynamic and solidification studies of continuous strip casting /." Luleå, 2000. http://epubl.luth.se/1402-1544/2000/30/index.html.
Testo completo
14
Delmont, Andres Emilio. "Shape distortion and air gap formation during continuous casting." Thesis, Sheffield Hallam University, 1985. http://shura.shu.ac.uk/19549/.
Testo completoAbstract (sommario):
A theoretical model has been developed which relates the build-up of stresses in the thin shell of steel solidifying in a continuously casting mould, to the shape distortion and the formation of an air gap. The work postulates that the behaviour of this shell can be analysed as that of a flexible structure formed by four elasto-perfectly plastic beams linked by rigid comers. This "box" represents the whole section of solidified shell at a given metallurgical height only if the section is totally detached from the mould. In general, it represents the detached corner portions alone. The rest of the shell is assumed to remain clamped against the mould wall by the metallostatic pressure. The thermal contraction of the neutral axis "filament" along the whole shell determines the amount of room which is available for the detached corner portion to distort, and thus also the size of the detached lengths of shell. The mechanical equilibrium of the structure is determined by the combined effect of temperature gradients and metallostatic pressure, by the rigidity condition imposed at the corner and by the flexural characteristics of the shell. The yield stress of the steel is assumed linearly dependent on temperature. The analysis of the shape distortion and air gap formation was initially informed by the observed behaviour of a partial physical analogue constructed from bi-metallic strips linked by rigid corners. Thermal moments were induced by immersing this analogue in a water bath at controlled temperatures, and distributed loads were imposed through a system of pulleys. The elastic behaviour of this physical analogue was predicted using basic beam theory. For the analysis of the deformation of a continuously cast structure, mathematical equations were derived which describe the overall moment and force equilibrium; the elastic and plastic stress distribution across the thickness of the shell; and the force and moment equilibrium within the cross-section of the shell. An equation was derived relating the curvature at any point along the shell to the moment at the corner of the structure. An iterative procedure was developed to determine the moment at the corner and a Runge-Kutta algorithm was incorporated to integrate the curvature equation. Further equations were derived which relate the deflection at the corner and the detached length on one side of the section, to the total length of the other side of the section. Recent high temperature studies of the mechanical behaviour of steels have been analysed in terms of the theoretical model developed. The model is able to predict the extent and thickness of the air gaps forming in the corner regions during the casting of billets and slabs and also provides explanation for the formation of both internal and external off-corner cracks. It also demonstrates the theoretical basis behind the practically observed relationship between casting speed and crack formation.
15
Jiang, Guang Sheng. "Inclusion behaviour in the liquid core during continuous casting." Thesis, Sheffield Hallam University, 1992. http://shura.shu.ac.uk/19876/.
Testo completoAbstract (sommario):
Water models using perspex have been built to study the fluid flow and recirculation patterns developed in the sump of a steel continuous casting machine and the influences these have on the behaviour of inclusions. An experimental method has been devised to simulate the behaviour of inclusions in the sump and to study the apportionment of the input flux of inclusions between the molten mould powder layer and the strand. The method entails the uses of finely dispersed coloured paraffin oil in the inlet stream together with a floating colourless paraffin layer on the top of the water in the model mould to simulate the molten powder layer on top of the molten steel. A theoretical model has been formulated which relates the inclusion separation in the sump to the fluid flow there. The inclusion removal ratio in the sump for a given continuous casting machine can be predicted using this theoretical model. The model, using the properties of liquid steel and practicable casting speeds, demonstrates that the removal of inclusions of small size (< 40 um) from the mould sump is less than 5% efficient. Inclusion agglomeration plays an important role in inclusion removal. It has been shown that deep submersion of the SEN enhances the agglomeration of inclusion particle. Under certain conditions, for example, the average particle diameter in the meniscus region has been found to be as much as three times its value at the SEN nozzle. The use of fine alumina flakes or small air bubbles, together with a plane light source, has been found to be very successful in studying the fluid flow patterns developed in three-dimensional models. Employing this method, the fluid flow patterns developed on different planes within the model mould have been viewed and recorded photographically. The photographs so obtained have helped to explain the results obtained for the removal of inclusions. The fluid flow patterns developed when small outside diameter nozzles with deep SEN submerged depths are used have been found to be of benefit to the removal of inclusions. Increasing the SEN submerged depth promotes inclusion agglomeration and hence increases the inclusion removal ratio. Reducing the nozzle outside diameter and the casting speed increases the inclusion removal ratio in the sump. But the infleunces of these latter changes are not very strong, so that inclusion removal consideration need not influence the design strategies used for the casting speed and nozzle outside diameter. The SEN port angle has a little effect on the inclusion removal when using deep SEN submerged depth. Although argon stream introduced into the tundish nozzle stream can protect the nozzle blockage, it is not beneficial to the inclusion removal in the sump.
16
Bommaraju, Ramaprasad V. "Mold behavior, heat transfer and quality of billets cast with in-mold electromagnetic stirring." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28628.
Testo completoAbstract (sommario):
Mold behavior, mold-related quality and the columnar-to-equiaxed transition influenced by in-mold EMS were examined by performing trials at two steel companies, metallurgical examination of the billet samples and mathematical modelling. The thermal fields in the walls of billet molds (102 X 102mm and 127 X 178mm) and in the cooling water were monitored by a system of thermocouples as the EMS was switched on and off during the continuous casting of several heats. The effect of electro-magnetic stirring on mold heat extraction was found to be negligible. The mold temperatures and cooling water temperatures are strongly dependent on the mold/billet gap which is affected by dynamic distortion of the mold tube. In the case of the square mold, the time-dependent mold distortion resulted from boiling adjacent to the cold face due to low water velocity and poor water quality. In the rectangular mold, differential expansion of the wide and narrow faces of the mold led to periodic wall movement at the midface causing cycling in the mold and water temperature. Both effects completely dominated any potential influence of EMS on mold heat extraction.
Cooling water velocities measured in separate experiments and the mold temperature profiles were input to a two-dimensional heat-flow model to establish mold heat-flux profiles. A steep taper of 2.6 %/m in the upper regions of the mold increased heat extraction compared to previously published heat-flux data in 0.8 %/m tapered-molds. However, due to the periodic wall movement in the rectangular mold, the heat flux declines to lower values periodically. The calculated heat flux profiles were employed in a one-dimensional transient heat flow model to predict superheat removal from the liquid pool under a variety of assumed fluid flow conditions. The major heat flow effect of EMS was inferred to be one of increasing the convective heat flow at the solidification front leading to earlier superheat extraction from the liquid steel.
Solidification structures in billet samples collected during the trials were examined. The columnar-to-equiaxed transition in continuous casting takes place provided all the superheat is removed from the melt and there is a sufficient density of nuclei present in the pool. At superheats of <20° C in the tundish, high heat extraction in the mold and remelting of the mold generated nuclei facilitate the removal of the superheat well within the mold and the columnar-equiaxed transition is triggered after 10-15 mm of shell growth on both the inside and outside radius faces. At higher superheat in the tundish, the liquid pool leaves the mold with residual superheat which takes longer to remove because of the declining fluid flow. Even though all the superheat is removed lower in the machine, the columnar-equiaxed transition occurs only if dendrite debris generated in the vicinity of the mold has survived in their descent through the superheated liquid. The effect of carbon on the columnar-to-equiaxed transition appears to stem from its influence on facilitating dendrite arm remelting and the survival of the dendrite fragments till the pool reaches sub-liquidus temperature. EMS extracts more superheat by maintaining a steep temperature gradient in the thermal boundary ahead of the solidification front and achieves an earlier columnar-equiaxed transition.
Electro-magnetic stirring appears not to affect either the average depth or the variation of depth of oscillation marks across a given face. However, the electro-magnetically driven flow dominates the turbulance at the meniscus due to the input stream and stabilizes a meniscus shape with the result that the oscillation marks are also of a well-defined shape unlike the unstirred billets.
No influence of EMS was found on the formation of "hooks" or the fine equiaxed crystal zone near the surface. The influence of EMS on inclining the growing dendrites appears to not come into effect until about 1 mm of shell has formed. It appears that the existence of the momentum boundary layer where the velocity of the rotating steel falls to zero at the surface is the reason for the absence of the influence of EMS on the subsurface solidification.
Rhomboidity and off-corner crack formation were found to depend, as reported by previous researchers, on mold distortion and its dynamic nature. The absence of any effect of EMS on these defects is due to its lack of effect on mold heat transfer and thus mold distortion.<br>Applied Science, Faculty of<br>Materials Engineering, Department of<br>Graduate
17
Henderson, Robert J. "Thermomechanics of multiphase refractories." Thesis, University of Aberdeen, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244992.
Testo completoAbstract (sommario):
Refractory materials must, in their everyday environment, withstand high stress levels which are a result of mechanical and thermal loadings. Any failure which results from these applied stresses can have serious financial and human consequences and therefore should be avoided. One key aspect to understanding the thermal shock behaviour of refractories is the mechanical behaviour at low temperatures. In this thesis the mechanical behaviour of a small range of multiphase refractories is explored. In particular the stress-strain response and its influence on the fracture behaviour is investigated. Experiments, performed on magnesia and magnesia spinel composites, indicate that non-linear stress-strain behaviour accompanied by permanent deformation upon unloading is a result of the release of microscale residual stresses by microcracking. A micromechanical constitutive model combining these features was developed using linear elastic composite theory and isotropic continuum damage mechanics. This non-linear stress-strain behaviour also gives rise to increasing toughness as crack propagation occurs. This increase in toughness results from an expansion which occurs when microscale residual stresses in front of the crack tip are relaxed by microcracking. A micromechanical model has been developed based upon the specifically developed constitutive model and previous work on transformation toughening. These models are capable not only of simulating experimental results, but can also indicate the microstructures which are most likely to exhibit extensive non-linear stress-strain behaviour and strongly rising toughness curves.
18
Mimura, Yoshihito. "Sticking-type breakouts during the continuous casting of steel slabs." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27941.
Testo completoAbstract (sommario):
Sticking of the shell in the mold, which often occurs in a high-speed continuous slab casting machine, can be detected with thermocouples in the mold copper plates and prevented from developing into a breakout by reduction of the casting speed. However, a rapid reduction of the casting speed causes some quality problems and a low slab temperature. Thus, sticking-type breakouts remain a concern to the steel industry, and it is still not clear how and why the sticking initiates at the meniscus. The objectives of this study were to identify the causes of sticking at the meniscus, to elucidate the mechanism of sticking and finally to propose methods to reduce the occurrence of sticking.
In order to identify the causes of sticking, it was necessary to examine a sticking-type breakout shell metallurgically, especially the dendrite structure at the shell surface. To link the metallurgical information to the casting conditions, the validity of a correlation in the literature between secondary arm spacing and local cooling rate has been examined. The secondary dendrite arm spacing in the subsurface of a slab has been measured and linked to a local cooling rate calculated from the measured mold heat-flux with this correlation. From this analysis, it was confirmed that Suzuki's correlation between secondary dendrite arm spacing and local cooling rate can be applied for a high cooling rate such as in continuous casting. A sticking-type breakout slab exhibiting five sticking events of 0.08% carbon steel, has been studied and it has been found that small holes exist at the surface in the sticking shells (most likely the site of entrapment, of solid mold flux). The shell which initially sticks exhibits a coarse dendrite structure and, in a longitudinal section, the shape of the initial sticking shell is parabolic. Moreover, with one exception, segregation lines typically 1-3 mm below the surface and almost parallel to the surface have been found in most of the sticking shell. From secondary ion mass spectroscope studies, the solutes concentrating in these segregation lines were determined to be Mn and S.
Apparently, the sticking occurs at the meniscus where heat extraction is greatest and molten mold flux flows between the shell and solid mold flux rim oscillating with the mold. Therefore, to explain these meniscus phenomena, mathematical models of heat transfer at the meniscus and fluid flow in the mold flux channel have been formulated. To analyze the initial sticking event, the meniscus level has been changed in the computer simulations and the following mechanism has been proposed to explain the initiation of a sticking-type breakout. If the meniscus level rises, a deep notch forms in the shell due to the interaction between the mold flux rim and the shell. When a thick mold flux rim moves downward, it contacts the shell above the notch and the shell sticks to the mold flux rim. During the upstroke motion of the mold, tensile forces on the shell cause a rupture at the deep notch which is the hottest and weakest. The predicted solid flux rim profile agrees well with the parabolic shell shape measured in a longitudinal section of the sticking shell.
Since the hot spot is the most likely point to be ruptured, conditions which minimize the hot spot were sought with the models. It was found that most of the conditions required to reduce hot-spot formation are exactly opposite to those required to minimize oscillation mark depth. Notwithstanding this, there are a few techniques to reduce the occurrence of sticking and to improve the surface quality: use a low melting point mold flux and, probably, maintain a deep mold flux pool. An interesting finding with respect to oscillation mark formation is that, if the mold flux rim is thick, the oscillation mark is caused by the interaction of the flux rim with the solidifying shell, while the fluid pressure development in the molten flux film dominates the mark formation in the case of a thin flux rim.
For the analysis of the segregation line, a mass transfer model has been formulated based on a consideration of δ — γ transformation. From this analysis, it was found that the segregation observed in the sticking shell is a band of interdendric segregation enhanced by enlarged primary dendrite arm spacing which, probably, is caused by the appearance of an air gap due to the shell shrinkage.<br>Applied Science, Faculty of<br>Materials Engineering, Department of<br>Graduate
19
Mahapatra, Rama Ballav. "Mould behaviour and product quality in continuous casting of slabs." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/29214.
Testo completoAbstract (sommario):
An extensive study has been conducted to elucidate mould behaviour and to examine its influence on product quality during continuous casting of slabs. The study essentially comprised of industrial measurements, mathematical modelling and metallographic examination. The industrial measurements consisted of mould temperature measurements; an operating slab mould was instrumented with 114 thermocouples and the temperature of the mould at different locations was successfully measured for a wide range of casting conditions. A three-dimensional heat flow model of the mould was developed to quantitatively characterize the heat fluxes in the mould from a knowledge of the mould temperature data. Futhermore, a one-dimensional solidification model was developed to simulate solidification of steel and also, a heat flow model was developed to examine the mould flux behaviour by characterizing the slag rim thickness at the meniscus. Slab samples collected during the industrial trial campaign were metallographically examined to study the different aspects of solidification in the mould, sub-surface structure, solidification bands, cracks and oscillation marks.
The thermocouple measurements revealed the occurrence of metal level fluctuation in the mould, the magnitude of which was appreciable. Thus, implementation of a metal level control system has been recommended. The time-averaged mould temperature data was converted into heat fluxes and it has been well demonstrated that a three-dimensional model of the mould wall was essential for accurate computation of heat fluxes in the mould. The measurements have clearly established the strong dependence of heat transfer in the mould on the mould flux employed during casting. A reduction in the viscosity and melting temperature of the mould flux will lead to enhancement of heat transfer in the mould. It was also found that the heat transfer in the mould can be influenced by changes in casting speed, submergence depth, steel carbon content; the effect of these variables on heat transfer has been explained mostly on the basis of their influence on the mould flux behaviour at the meniscus. Furthermore, heat extraction characteristics on the two broad faces were different which was a consequence of differences in mould flux behaviour resulting from differences in mould wall thickness between the two broad faces.
The heat-flux profiles were employed as a boundary condition in the solidification model to compute the shell thickness in the mould for a wide range of casting conditions. The casting speed has a significant influence on the shell profile in the mould; an increase in the casting speed led to a reduction in the shell thickness. The non-uniformity of the shrinkage of the solid shell in the mould was evident from the slab surface-temperature profile which clearly revealed the advantages of a non-linear taper of the narrow face compared to the conventional single taper. From a knowledge of heat-flux profile and metallographic analysis, a mechanism towards formation of longitudinal cracks/depression was formulated. Mathematical analysis performed on the mould flux at the meniscus revealed the presence of a slag rim adjacent to the mould wall; the dimensions of the slag rim thickness were computed at different casting speed and mould wall thickness. It was shown that oscillation marks are formed by the interaction of the slag rim with the partially solidified meniscus; the depth of the oscillation marks is strongly governed by the thickness of the slag rim at the meniscus.
This study has unambiguously shown that the dimension of the slag rim at the meniscus is quite critical from the standpoint of heat transfer and product quality of slabs. Based on the findings of the present study, for the first time, links have been established between the mould wall thickness and heat transfer in the mould. The slag rim thickness at the meniscus can be reduced by increasing the mould wall thickness. It is anticipated that an increase in the casting speed and thus, a corresponding increase in production rate can be accomplished by changing the design of the mould.<br>Applied Science, Faculty of<br>Materials Engineering, Department of<br>Graduate
20
Miao, Xincheng. "Numerical study of a continuous casting process with electromagnetic brake." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-144798.
Testo completoAbstract (sommario):
This dissertation investigates the effect of electromagnetic braking and gas injection on the fluid flow in a continuous casting slab mold numerically and makes verifications on basis of a small Liquid Metal Model for Continuous Casting of steel (mini-LIMMCAST). Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. The numerical results were validated by flow measurements at the mini-LIMMCAST facility. Numerical simulations disclose the damping effect on the flow closely depending on the wall conductance ratio. In addition, specific modifications of the turbulence model play a crucial role in reconstructing the peculiar phenomenon of an excitation of nonsteady, nonisotropic, large-scale flow perturbations caused by the application of the DC magnetic field.
21
Barreto, Sandoval Jose de Jesus. "Model studies of plasma heating in the continuous casting tundish." Thesis, Sheffield Hallam University, 1993. http://shura.shu.ac.uk/19322/.
Testo completoAbstract (sommario):
A room temperature water model of a tundish was design, constructed and operated. The model was equipped with a steam heating system that simulates that simulates the tundish plasma heating systems operated by some of the more modem continuous casting plants. Similarity between steam heating in the water model and plasma heating in the tundish has been established. A dimensionless criterion was developed to validate the simulation experiments and its represented by the plasma heating number. Using this similarity criterion plasma heating can be simulated by steam heating in an appropriately designed water model. A theoretical dispersion model has been formulated for the flow through the tundish and the parameters in this model determined from the results obtained from residence time distribution measurements. A conductivity method was used, a highly conducting species being injected at the inlet point and changes in conductivity monitored at the exit. Measurements were also made of the changes in temperature at the exit resulting both from changes in temperature of the inlet stream and from the use of steam heater system. A stable inverse heat conduction method has been developed in which the measured and estimated temperature are analysed in terms of a steady components of short duration. A finite difference method has been used to predict the effect on a thermocouple temperature of the deviatory components of the liquid steel temperature. The incorporation of these predictions into look-up tables has allowed an algorithm to be developed thet can deduce the current deviatory component of the steel temperature from the thermocouple response.
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Ávila, Braz Thaís. "Shrinkage Calculation in the Continuous Casting of Duplex Stainless Steel." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76516.
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Short, David James. "Swirling flow induced by a rotating magnetic field." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338644.
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Leckenby, B. M. "Finite element analysis of bulging during the continuous casting of steel slabs and blooms." Thesis, University of Sunderland, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382766.
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Bradbury, Philip. "A mathematical model for the twin roll casting process." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296919.
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26
Aboutalebi, M. Reza. "Modelling of turbulent transport phenomena and solidification in continuous casting systems." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41514.
Testo completoAbstract (sommario):
A numerical modelling study has been undertaken to analyze transport phenomena in various steel casters. During the course of this work, a general three-dimensional parabolic heat flow model was developed for casters of arbitrarily shaped mould using a body-fitted coordinate transformation technique. The heat flow model was specifically applied to a beam blank caster as well as to an industrial slab caster of regular rectangular cross section, so as to analyze solidification within casters.<br>Furthermore, a fully coupled turbulent flow and solidification model was developed to describe the turbulent transport processes in the upper part of a steel slab caster as well as to evaluate the process variables affecting the casting. Solidification modelling was carried out using a fixed grid enthalpy method while the mushy zone was modelled based on a Darcy-porosity approach. A modified low-Reynolds number version of the $ kappa$-$ epsilon$ model of turbulence was employed to calculate eddy viscosity within the liquid and mushy regions. A control volume based on finite difference method was used to solve the transport equations, wherein a SIMPLER algorithm was adopted to resolve the velocity-pressure coupling in the momentum equations. In order to verify the turbulent flow model, a water modelling study was performed for fluid flow in the mould region of a slab caster. Reasonable agreement was obtained between the mathematical model's predictions, and water modelling experiments.<br>Macrosegregation of carbon in a steel billet caster was also modelled based on a continuum formulation, in which the conservation equations are derived in terms of mixture dependent variables. The effect of turbulence on the transport of solute in the liquid and mushy regions was taken into account using the $ kappa$-$ epsilon$ model adopted in this work.<br>Various parametric studies have been preformed on different casting systems, and their effects on temperature distributions and velocity fields within the strand, solidification profiles, and trajectories of inclusions were predicted. Typical predicted results of the models have been compared against the experimental measurements on operating casters reported in the literature and relatively good agreement was obtained.
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Chakraborty, Sanjib. "Melt flow and heat transfer in continuous casting ladles and tundishes /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487694389392267.
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Yao, Peiling. "A Fundamental Study On Life Assessment of Continuous Slab Casting Rolls /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487933245537544.
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Kountouriotis, Zacharias. "Modelling of the liquid slag behaviour in the continuous casting mould." Thesis, University of Greenwich, 2011. http://gala.gre.ac.uk/7658/.
Testo completoAbstract (sommario):
This work presents a fluid dynamics model of a continuous caster mould region, including the transient behaviour of the steel/slag interface. The research was carried out in collaboration with ArcelorMittal Research (AMR), based in Maizieres-les-Metz in France. The industrial objective of the thesis was to understand the factors affecting the transient behaviour of the liquid slag layer covering the steel and its interaction with the Submerged Entry Nozzle (SEN) jet supplying the steel from the tundish to the Continuous Casting (CC) mould. The study includes the very complex phenomenon of argon bubble transport which also affects the behaviour of the slag layer and SEN jet. The model developed in this study is based on the finite volume method with the liquid regions (steel, slag) solved in an Eulerian scheme on a fixed unstructured mesh. The interface behaviour is modelled using a number of VOF type schemes, including the time-efficient Counter Diffusion Method (CDM). A coupled Lagrangian particle tracking scheme is used to represent the presence of argon bubbles and their influence on the flowfield (mainly due to buoyancy) in conjunction with the fluctuating surface dynamics. The bulk of the research concerns comparisons against flowfield and interface data obtained from an experimental water/oil study of the process. However, the model is extended to include predictions of heat transfer and phase change in the steel and flux powder regions in an industrial CC unit and validation against available data. The three-phase model is developed making use of the unstructured mesh multi-physics finite volume code PHYSICA [1]. As stated, the main goal of this particular work has to do with the study of the dynamic behaviour of the steel/slag interface, including the effects of casting speed and injected gas. Because of the great difficulty in physical experiments with a real caster, the research is supported with water model experiments and mathematical simulation. Comparisons of observed interface profiles, measured and predicted mean and fluctuating velocities, gave an insight to the degree of coupling between interface behaviour and the fluid dynamics within the mould region. In particular, a spectral analysis of the dominant fluctuation frequencies in the water/oil experiment suggests a strong link between the upper and lower recirculation loops generated by the SEN jet as it splits after contact with the narrow face for the mould. The presence of gas bubbles alters the spectral picture, since the buoyancy induced in the flow affects the behaviour of the jet, leading to the one/two loop behaviour known from experiments. Good qualitative and quantitative agreement was achieved between the numerical results and water-model experimental data. The main observations drawn from the water model simulation and experiment are as follows: - An increase in casting speed, which is equivalent to an increase in SEN velocity leads to an increase in the amplitude of interfacial fluctuations. - At the highest SEN velocities, the oil layer is pushed away from the narrow ends of the mould, exposing the water surface to air. - When there is no oil on top of the water surface, the surface remains for all practical purpose flat. - Air entering through the SEN influences the flowfield in the mould and also disturbs the oil/water interface when it passes through it. - The ratio of water to air flow rate seems to be the most important parameter, with high air/water flow ratios leading to a change in flowfield at the top of the mould as the gas buoyancy lifts the SEN jet towards the surface. To achieve a good correlation between the experiments and the simulations a number of factors in the numerics were found to be important. These are: - The quality of the mesh used, especially in the complex transition from the SEN geometry – essentially a cylinder with two outlets set at a specific angle of 20o to the vertical, to the thin rectangular geometry of the mould which is designed to cast flat products. - The turbulence model, which was initially found to suppress interface oscillations whenever an oil layer was introduced. Various approaches were followed to overcome this problem, (a)removing the turbulence model from the oil layer, (b) using a low frequency filter to remove resolved turbulence kinetic energy from the k-ε model, (c)opting for the high order SMART numerical scheme in preference to the default Hybrid. - The interface tracking algorithm used as a default in the code PHYSICA is essentially a VOF technique with options for a Van-Leer (TVD) scheme [2] or alternative the popular Donor Acceptor scheme [3,4], both options work well but they are explicit and therefore extremely expensive computationally. Due to the size of the mesh and the CFL limit for stability, timesteps as small as 10-3s become necessary, meaning a 600s simulation could take up to 8 weeks! To overcome this, the implicit CDM scheme [5] was used, which allows the interface to spread by diffusion but then pushed back against the gradient to re-sharpen at the end of each timestep. With this scheme, timesteps up to 2 orders of magnitude larger become possible, the limit then governed by the frequency range to be resolved. A non-standard approach to the Lagrangian particle tracking scheme was adopted in the simulation with the following characteristics: - The amount of gas entering was divided into packets of equal bubble diameter and then each packet was further divided into individual tracks. The transport of 1000 and more particles tracks was used to ensure a realistic dispersion. - Tracks were updated at regular time intervals (but not necessarily at each Eulerian timestep) and then followed until they exited the calculation domain. - The residence time of particles in each cell provided information for the gas content of the cell and therefore its density. With this approach, the Navier-Stokes equations then solve for mixture (gas and liquid) and lighter cells are influenced by buoyancy. - The bubble tracks are affected by the mean velocity of the surrounding fluid and also by a stochastic component derived from the turbulence model. However, there is no direct feedback to fluid turbulence from the bubbles. To extend simulations to a real caster, heat transfer and phase change were introduced in the model, in addition to the property changes (water to steel, oil to slag, air to argon). Of importance here was the development of a solidified skin of steel on the water-cooled mould walls and also the melting of flux powder into a liquid layer on the top surface. This last component of the research was introduced to enable comparisons against plant data obtained by AMR. Of particular interest in this study was the transition from a double to a single roll recirculation in the top section of the mould, as a function of the relative quality of argon entering the SEN. The model was able to reproduce this behaviour for the cases studied. Although much has been done in developing this model of the continuous casting process it is evident that much more research is needed, especially in the case of a real caster. For example, the thermophysical property variations in the slag due to temperature, composition and mass transfer were ignored. A very simple approach was used for the phase change in steel and flux powder, although since the PHYSICA framework is modular, more sophisticated alternatives can be easily introduced. The boundary conditions for heat transfer remain uncertain and the values used in this study were obtained from the industrial partner from earlier experiments. In spite the aforementioned limitations, the model is very useful, especially in understanding the dynamic interactions between the SEN jets, and the slag/steel interface and in this respect in advance of other models used by industry.
30
Du, Pengfei. "Numerical modeling of porosity and macrosegregation in continuous casting of steel." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/2482.
Testo completoAbstract (sommario):
The continuous casting process is a widely used technique in modern steel plants. However, it is a complicated process that is not well understood. The objective of this research is to model the porosity and macrosegregation due to shrinkage related effects and solid deformation in the continuous casting of steel.
Solid phase movements due to bulging and variable roll gap are modeled with a simple algebraic equation based on assumed slab surface deflection. A simplified single domain fluid flow model is derived to predict the pressure field. When liquid pressure drops to zero, porosity starts to form. The distribution of porosity is calculated using the porosity equation which is based on the mass conservation. A macrosegregation model based on the species conservation is derived. With the relative velocity calculated from the pressure results and the solid velocity, macrosegregation is obtained. Since the solid phase velocity is not zero and mixture density is not assumed to be constant, porosity and macrosegregation due to both solid deformation and shrinkage effects are incorporated.
In order to validate the model, the pressure field of a three-dimensional pure metal solidification system is simulated. The results show the feasibility of the proposed model to predict the fluid flow. The porosity and macrosegregation prediction for different casting conditions are performed. The results confirm the necessity of including solid phase deformation in the prediction of porosity and centerline macrosegregation. The results also reveal the relations between different operating conditions (such as degree of bulging, soft reduction, and casting speed) and the porosity/macrosegregation defects in the final product.
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Lester, Samuel John. "Laser cladding to improve the campaign life of continuous caster rolls." Thesis, Swansea University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.660122.
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De, Wet Gideon Jacobus. "CFD modelling and mathematical optimisation of a continuous caster submerge entry nozzle." Pretoria : [s.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-01312006-141026.
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Almeida, Leandro de. "Estudo comparativo da estampabilidade do latão UNS C22000 produzido inicialmente pelo processo de fundição contínua em comparação a fundição semicontínua." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-01092017-160621/.
Testo completoAbstract (sommario):
As curvas limite de conformação (CLC) são utilizadas há mais de 50 anos. Propostas inicialmente para o desenvolvimento de produtos provenientes da indústria automobilista em função das necessidades apresentadas pela área, são atualmente aplicadas de maneira geral para a indústria da estampagem na produção de inúmeros tipos de peças, oferecendo previsões de possíveis falhas e/ou defeitos durante as etapas do processo de estampagem. As CLC´s permitem prever o afinamento excessivo, enrugamento, estiramento e é claro, a fratura da peça. As diferenças metalúrgicas existentes entre os dois processos iniciais - fundição contínua (F.C.) e fundição semicontínua (F.S.C.) - resultam em diferenças nas propriedades finais obtidas para uma mesma rota de laminação a frio e recozimentos intermediários do material especificado. Desta forma, torna-se indispensável um estudo sobre a influência dos processos de fabricação iniciais F.C. e F.S.C. com relação à estampabilidade da liga, sendo esta avaliação efetuada através das CLC´s obtidas por ensaios de tração uniaxiais, propostos pelo IRSID (\"Institut de Recherches de La Sidérurgie\"), (lado esquerdo da curva ?2 < 0) e ensaio Erichsen (lado direito da curva ?2 > 0) e do ensaio de Nakazima reduzido em 60%, ou seja, todo o ferramental e os corpos de prova utilizados nos ensaios foram reduzidos em 60% das dimensões mencionadas pela norma ISSO 12004-2. A diferença microestrutural apresentada entre as etapas de fabricação dos dois processos avaliada através de ensaios de determinação do tamanho de grão, limites de resistência à tração, escoamento (0,2%), alongamento (em 50,80 mm), coeficientes de encruamento n, resistência K, ensaios de \"orelha\", levantamento da CLC0, Erichsen e textura, auxiliaram nas conclusões finais do levantamento das CLC´s para os dois processos do material acabado e metodologias. O processo de fundição semicontínua nas condições processadas apresentou melhores combinações entre as propriedades, exceto na formação de \"orelha\" apresentada na etapa intermediaria de processamento do material. Principalmente o parâmetro CLC0 no plano da chapa, resultou em uma deformação ?1 19% (?2 = 0), superior à apresentada pelo processo F.C., deformação muito importante para a fabricação de peças estampadas. Evidenciou-se também uma diferença de aproximadamente 37% entre as metodologias IRSID x Nakazima reduzido na obtenção da deformação plana para o processo F.C. e 31% para o processo de F.S.C.. Nas condições de deformação; estiramento biaxial, tração uniaxial e embutimento profundo, a chapa produzida pelo processo de fundição contínua apresenta melhor desempenho.<br>Forming limits curves (FLC) are used for more than 50 years. Initially proposed for the development of products from the automobile industry in terms of the needs of the area. It is currently being applied in general to the metal forming industry in the production of numerous types of parts, providing predictions of possible faults and / or defects during the stages of the stamping process. The FLC\'s can predict excessive thinning, wrinkling, stretching and of course, the fracture of the part. The existing metallurgical differences between the two initial processes - continuous casting (C.C.) and semi-continuous casting (S.C.C.) - result in differences in the final properties obtained for the same route of cold rolling and intermediate annealing of the specified material. Thus, it is essential to study the influence of the initial manufacturing processes CC and SCC with respect to the formability of the sheets. This investigation is based on the, assessment of the FLC\'s obtained by uniaxial tensile tests proposed by IRSID (\"Institut de Recherches de Sidérurgie\"), (?2 < 0, left side of the curve) and Erichsen test (right side of curve. ?2> 0) and the Nakazima test reduced by 60%. The difference between the sheets obtained in both processing routes was evaluated by the following parameters: grain size, tensile strength limits, yield strength (0.2%), elongation (at 50.80 mm), strain hardening coefficient n, resistance K, \"earing\" test, lifting of the CLC0, Erichsen test and texture where discussed in view of the obtained FLC\'s for both the two processes of the finished material. The semi-continuous casting process in processed conditions showed better combinations of properties except the formation of \"earing\" presented at the intermediate stage of processing of the material. Particularly the evaluation of the FLC0 parameter resulted in a strain in the plate plane ?1 19% (?2 = 0) superior to the sheet obtained by the continuous casting process. A difference of approximately 37% between the IRSID x Nakazima methodologies was also reduced in obtaining the flat deformation for the F.C. process and 31% for the F.S.C. process. However, for other deformation paths; biaxial stretching, uniaxial traction and deep drawing of the results for the continuous casting sheet were superior.
34
Carpenter, Kristin. "The influence of microalloying elements on the hot ductility of thin slab cast steel." Department of Materials Engineering - Faculty of Engineering, 2004. http://ro.uow.edu.au/theses/161.
Testo completoAbstract (sommario):
Experiments were preformed on a Gleeble 3500 Thermomechanical Simulator to study the hot ductility behaviour of C-Mn-A1 steel and the influence of Nb, Ti and Nb-Ti additions. The simple hot tensile test has been shown to correlate well to the problem of transverse cracking. Therefore, the principle aim of this research is to gain a greater understanding of transverse cracking during the straightening of continuously cast slabs. In particular, attention was paid to thin slab casting conditions. Hot tensile test specimens were either solution treated in melted in-situ (direct cast) and cooled to the deformation temperature. Solution treatment tests simulated conventional casting, where slabs are cooled to room temperature than heated prior to rolling. Direct cast tests simulated hot direct rolling conditions, where slabs are rolled directly after casting without being cooled below the austenite to ferrite transformation. Specimens were cooled to the deformation temperature at two cooling rates, 100K/min and 200K/min. The cooling rate of 100K/min corresponds to the average cooling rate experienced for a conventionally cast slab, 250mm in thickness. The cooling rate of 200K/min corresponds to the average cooling rate for thin-cast slabs, 50mm in thickness. The development of the combination of thin slab casting of hot direct rolling requires hot ductility work to be performed under direct cast conditions and at higher cooling rates. Surface quality is of the utmost importance in thin slab casting so the elimination of transverse cracking is of prime economic importance. There are significant differences between as-cast (direct cast) and reheated (solution treatment) microstructures. In particular, changes in precipitate behaviour, austenite grain size, and the relationship between segregation and the position of austenite gran boundaries was investigated. An attempt has been made to determine what influences these differences in microstructure have on hot ductility. Niobium bearing steels were selected for the reason that there are still problems with Nb steels regarding transverse cracking. Furthermore, there have been contradictory reports on the effects of Ti additions on the transverse cracking behaviour of NB steels. There is evidence from commercial practice that indicates that small additions of Ti improve the transverse cracking susceptibility of Nb steels. However, laboratory results generally show Ti additions have little influence or even a detrimental effect on hot ductility. Disparities in the thermal history simulated in laboratory tests to actual conditions near the surface of a continuously cast slab is the most likely reason for this discrepancy. Therefore, the influence of more closely simulating the thermal history conditions near the surface of a continuously cast slab was evaluated for the Nb-Ti steel. Experimental work involved metallographic and scanning electron microscopy examination of the fracture surface. Transmission electron microscopy was used to determine precipitation characteristics. Tensile tests were conducted to determine mechanical properties, where reduction in area (RA) was used as a measure of ductility. The dendritic structure for direct cast and solution treatment specimens was revealed using a heat treatment procedure (normalising). Particle size was correlated to reduction of area for precipitates in the single-phase austenite temperature region. It was shown that particles below 15nm were detrimental to hot ductility. The relationship between interparticle spacing and reduction of area was also determined. Microalloying additions to C-Mn-A1 steels significantly widen the ductility trough but the depth remains similar. Low ductility was found at higher temperatures in the microalloyed steels due the intergrandular failure as a result of grain boundary sliding in the austenite. Grain boundary sliding was favoured by the slow strain rate and was enhanced by fine microalloyed nitrates and/or carbides. Fine particles can pin austenite grain boundaries, allowing sufficient time for cracks to link together, ultimately causing intergranular fracture. Increasing the cooling rate generally lowered ductility further by promoting finer precipitation. The trough depth is similar in all steels as the formation of thin ferrite films controls ductility at the minimum trough position. The formation of thin films of ferrite allowed strain to concentrate in the softer ferrite phase and intergrandular failure occurred due to microvoid coalescence. Direct cast conditions always led to lower ductility compared to solution treatment conditions. This is explained in terms of differences in the microstructure, namely, grain size, segregation and precipitation. It is recommended that direct cast conditions should be used to determine hot ductility behaviour as it more accurately simulates continuous casting conditions. It was found that simulating the thermal history near the surface of a continuously coast slab, as opposed to cooling directly to the deformation temperature, improved ductility of the Nb-Ti steel. This improvement in ductility was attributed to the thermal history providing favourable conditions for coarsening of NbTi (C,N).
35
Bouhouche, Salah. "Contribution to quality and process optimisation in continuous casting using mathematical modelling." Doctoral thesis, [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=966041208.
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Bouhouche, Salah. "Contribution to quality and process optimisation in continuous casting using mathematical modelling." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2009. http://nbn-resolving.de/urn:nbn:de:swb:105-6900128.
Testo completoAbstract (sommario):
Mathematical modelling using advanced approach based on the neural networks has been applied to the control and the quality optimisation in the main processes of steelwork such as the ladle metallurgical treatment and continuous casting. Particular importance has been given to the improvement of breakout prediction system and the reduction in the rate of false alarm generated by the conventional breakout detection system. Prediction of the chemical composition and temperature of liquid steel in the ladle has been achieved by neural networks and linear model. This prediction can be considered as a soft sensor. Slab surface temperature stabilisation on the basis of the casting events has been controlled by a neural networks algorithm, that gives an improvement in the surface temperature fluctuation in comparison to the conventional control system which is based on the PID controller. Quality monitoring and classification is also achieved by a neural network which is related to the breakout detection system. This technique achieves a classification of different defects based on the different alarm signal given by the breakout prediction system. Fault detection and process monitoring is developed using neural networks modelling. All models are developed on basis of practical operating database obtained from the iron and steel industry.
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Elahipanah, Zhaleh. "Thermo-Physical Properties of Mould Flux Slags for Continuous Casting of Steel." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-101270.
Testo completoAbstract (sommario):
Due to the high efficiency and productivity of continuous casting process, this method has been the most employed process to produce steel in past decades. The need to improve and optimize the finished product made it essential to gain more knowledge about the process, types of defects that may occur and the reasons for them. Moreover, the solutions for reducing the shortcomings in continuous casting process have been an intriguing subject to study. Many attempts have been done in order to reach this goal. Understanding, determining and optimizing the mould flux slag properties is especially important, since it plays an important and significant role in this process. For this, it is of outmost importance to acquire more knowledge about different properties of mould flux powders. Hence, there has been a world wide effort to measure and model the properties of mould flux properties, such as liquidus and solidus temperatures, heat capacity, enthalpy, thermal expansion, density, viscosity, electrical conductivity, surface tension and thermal conductivity. This thesis presents a brief review on continuous casting process, mould flux powder and its properties and characteristics. Furthermore, it focuses on the thermo-physical properties of mould fluxes. In present work, different industrial mould flux powders have been analyzed to measure their viscosity, break temperature, physical properties such as density, flowablity of powder, slag structure and chemical composition. The experimental data have been compared to some of the most commonly used models such as Riboud model, Urbain model, Iida model and KTH model.
38
Yu, Peter Tong-Kan. "Simulation of transport phenomena during phase change in continuous casting of steel." Thesis, University of Ottawa (Canada), 1985. http://hdl.handle.net/10393/4675.
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Yamauchi, Akira. "Heat transfer phenomena and mold flux lubrication in continuous casting of steel /." Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3121.
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Sinton, David A. "Computational modelling of solid-liquid phase change with applications to continuous casting." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33346.
Testo completoAbstract (sommario):
An adaptive-grid numerical method for the computer simulation of steady-state, two-dimensional, solid-liquid phase change systems is presented. The grid is designed to delineate the solid-liquid interface using a structured adaptation technique. The fluid flow and thermal fields are solved concurrently using a control-volume finite element method. Of particular interest is the modelling of industrial solidification processes, such as the continuous casting of metal.<br>The combined adaptive-grid, CVFEM method is formulated for the solution of two-dimensional planar and axisymmetric problems. The proposed method is tested by application to natural convection in closed solid-liquid systems. Test problems in two-dimensional rectangular, cylindrical, and spherical axisymmetric enclosures, are presented.<br>An analytical solution of an idealized, one-dimensional, steady-state, continuous phase change process is derived. The numerical method is further tested with this analytical solution, and then applied to the continuous casting of aluminum into a cylindrical ingot. Comparisons of the calculated solid-liquid interface geometry with those reported in earlier experimental and numerical studies are encouraging. In addition, the role of natural convection in this casting process is investigated and presented.
41
Hill, N. J. "Visco-plastic and thermal stress analysis in the continuous casting of steel." Thesis, Teesside University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376088.
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Pimenta, Paulo Vicente de Cassia Lima. "Thermomechanical simulation of continuous casting process using element based finite-volume method." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=13684.
Testo completoAbstract (sommario):
CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior<br>The continuous casting technique in the last four decades has been large used for to production of semi-finished steel. The heat transfer is major mechanism and it occurs in various steps during the continuous casting. The quality of steel is directly related to the way the heat transfer occur because the thermal variations produce mechanical loads as well as contact forces which are generated through the rollers and shake of the mold. Such factors may cause defects such as fractures or cracks in the final product if the resulting stresses and strains exceed critical values. The technique must be improved in order to reduce the appearance of defects and the production time. For this a good understanding of physical phenomena involved during the solidification process is critical. The focus of this work is to apply the EbFVM (Element based Finite-Volume Method) approach to study the effects of linear tensions unidirectionally coupled with the temperature applied to continuous casting of the steel 1013D (0,3% of carbon)
In the simulations we adopted some simplifications such as the Plane Strain and isotropic material. We also neglected the body forces contact with the rollers the liquid pressure on the walls of the steel ingot (ferrostatic pressure) and the convective effect. However despite of the simplifications adopted this work provides quantitative informations on the linear tensions accumulation that point out to areas of possible of cracks formations<br>A tÃcnica de lingotamento contÃnuo nas Ãltimas quatro dÃcadas à cada vez mais utilizada na produÃÃo de aÃo semiacabado. A transferÃncia de calor à o principal mecanismo dominante e ocorre em todas as etapas do processo. A qualidade do aÃo no lingotamento està diretamente relacionada à forma que ocorrem as trocas de calor pois as variaÃÃes tÃrmicas produzem carregamentos mecÃnicos assim como as forÃas de contato as quais sÃo geradas por intermÃdio dos rolos e da oscilaÃÃo do molde. Tais fatores podem causar defeitos como fraturas ou trincas no produto final caso as tensÃes e deformaÃÃes resultantes excedam valores crÃticos. O aprimoramento da tÃcnica tem a finalidade de evitar o surgimento de defeitos e reduzir o tempo de produÃÃo. Para isso à fundamental uma boa compreensÃo dos fenÃmenos fÃsicos envolvidos ao longo do processo de solidificaÃÃo. O foco deste trabalho à aplicar a abordagem do EbFVM (Element based Finite-Volume Method) no estudo dos efeitos das tensÃes lineares acopladas unidirecionalmente com a temperatura aplicado ao lingotamento contÃnuo do aÃo 1013D (0,3% de carbono)
Nas simulaÃÃes adotou-se algumas simplificaÃÃes com o estado plano de tensÃes e isotropia do material. Descartando-se as forÃas de corpo o contato com os rolos a pressÃo do aÃo lÃquido nas paredes do lingote (pressÃo ferrostÃtica) e o efeito convectivo. Contudo apesar das simplificaÃÃes adotadas este trabalho traz informaÃÃes quantitativas quanto a formaÃÃo do acÃmulo das tensÃes lineares que apontam para regiÃes de possÃveis formaÃÃes de trincas
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Fan, Jia Su. "An investigation of the cracking mechanism in continuous casting rolls during service /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487684245467469.
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Brash, Benjamin. "Distortions of Press Quenched Crown Wheels." Thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-170022.
Testo completoAbstract (sommario):
Scania has experienced difficulties with large variations of the slope of the back plane after press quenching of case hardened crown wheels of especially type R780 Steg supplied from ingot cast material. This leads to that a large number of crown wheels has to be remeasured and sorted according to back slope which is time consuming for operators. Also, after sorting of the crown wheels, hard machining has to be adjusted according to the different slopes of the back plane of the crown wheels. In some cases, it also leads to scrapping of the crown wheels.This master’s thesis was divided in two parts. The aim of the first part was to confirm that the crown wheel type and casting technique that exhibits the largest variations in slope of the back plane is the R780 Steg originating from ingot cast material. The crown wheel types that were compared were the R780 Steg, R780 Slät and R885 Slät. Crown wheels manufactured from ingot cast material and from continuous cast material were compared. Hence, 6 combinations were examined. The slope of the back plane was measured with the measuring probe FARO after press quenching. The slope of the crown wheels was found to depend on both casting technique and the geometry of the crown wheel. The results confirmed that the crown wheel type and supplier combination that by far yields the largest variations in slope of the back plane is the R780 Steg supplied by Steel Plant A who uses the ingot casting technique. For this combination the variation exceeds 0,1 mm. All other combinations of crown wheels and suppliers yield acceptable variations.The second part of this master’s thesis was composed of determining if segregations in the cast ingot are the cause of the variations in slope of the back plane of the crown wheel type R780 Steg. This was done by measuring if there is a correlation between the slope of the back plane of the crown wheel after press quenching, the chemical composition and the original position of the crown wheel in the ingot. As in the first part of the study, the distortion was measured by the measuring probe FARO. The samples were sent to Degerfors Laboratorium for chemical analysis. Analyses of C, S and N were made by using combustion analyses. For As, P, B and Al optic spectrometry (spark) was used. All other elements were analysed by x-ray fluorescence. Segregations were found to be present and in combination with the geometry of R780 Steg to be the cause of the large variations in slope of the crown wheels.The results of this thesis show that, for the crown wheel type R780 Steg, Scania should not use suppliers that employ the ingot casting technique. Instead, only suppliers using the continuous casting technique should be used. However, for the other crown wheel types ingot or continuously cast material can be used.
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Barestrand, Henrik, and Tobias Forslund. "Numerical & physical modelling of fluid flow in a continuous casting mould : Flow dynamics studies for flexible operation of continuous casters." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-59847.
Testo completoAbstract (sommario):
The current demands on Swedish steel industry to produce low quantity batches of specialized products requires research on steel casting processes. There are several physical processes that need be taken into account for this problem to be viewed in full light such as thermal-processes, solidification and fluid dynamics. This work focuses on the fluid-dynamics part; more specifically, the dependence of flow quality within the caster on nozzle and mould geometry. The simulations are carried out using a scale-resolving method, in specific LES (Large Eddy Simulation) which is coupled with a DPM (Discrete Phase Model) to model Argon behaviour. The results of these simulations are presented and validated against physical experiment and data from industrial trials. Conclusions are drawn regarding optimal nozzle types in respect to different mould geometries. The mould eigenfrequencies are shown to exhibit a connection with the casting velocity. This results in so called sweet spots in casting velocity where flow irregularities due to sloshing is minimal. It is shown that the mountain type nozzle is preferable for smaller geometries whilst comparatively larger geometries benefit from a cup type.<br>FLOWFLEX CC
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Gupta, Debabrata. "Numerical simulation of unsteady state heat transfer in horizontal continuous casting with cyclic withdrawal." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185352.
Testo completoAbstract (sommario):
Solidification during horizontal continuous casting of low carbon steel billets with cyclic withdrawal was simulated and the wavy profile of the solidifying shell characteristic of this process was reproduced. Effects of rate of withdrawal cycle, superheat and casting speed were determined. In order to carry out this simulation in a personal computer, efficient numerical techniques had to be developed for mesh refinement by coordinate transformation, interfaces with temperature discontinuities and re-entrant corners. A flexible means of mesh generation involving polynomials was also developed. From the transient heat transfer model finite difference equations peculiar to each gridpoint in the solution field were derived and solved by the Alternating Direction Implicit (ADI) method. Graphics software were developed to view the results with 3-D as well as contour plots. The heat transfer model was verified with published results of vertical continuous casting of Mg alloys and steel. Due to its ability to deal with interfaces, unlike previous work, the present model could solve temperature at both casting and mold simultaneously. A model for the shell growth, rupture and healing at the break-ring of horizontal continuous casting molds was incorporated into the heat transfer model. An interesting result of this simulation was the presence of transient hot spots in the hot face of the mold. Elimination of such hot spots should aid shell strength and hence the casting rate. A semi-quantitative dependence of the depth of the primary witness mark on cycle rate was also established.
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Siyasiya, Charles Witness. "The transformation behaviour and hot strength of 3CR12 during the continuous casting process." Diss., Pretoria : [s.n.], 2004. http://upetd.up.ac.za/thesis/available/etd-06202005-134528.
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XU, TIJIE. "Detection of Final Solidification Due to Variation of Ferrostatic Pressure during Continuous Casting." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-215960.
Testo completoAbstract (sommario):
This paper presents an investigation on using the variation of ferrostatic pressure exerted by the molten steel in the strand to the support rolls during continuous casting to detect the location of the final solidification. The final solidification point is of high importance for applying soft reduction during continuous casting in order to ensure inner quality and achieve high productivity. The measurement was conducted at one of the casters at SSAB Oxelösund, of which all the support rolls are separately mounted. The project finds that this method shows promising results and can help to narrow down the range of the location due to certain interferences and noises. The ferrostatic pressure decrease during tail-out and the variation of whether a pressure drop exists is the dividing line of full and partial solidification. With the promising results achieved, more effort should be put to further improve the method.
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Saraswat, Rajil. "Modelling the influence of mould flux on steel shell formation during continuous casting." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434907.
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Damle, Chandrashekharr. "Melt flow, mixing and grade change studies in the continuous casting of steel /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487859313344697.
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